Question

A small ball carries a charge equal to 'e' Coulomb, where 'e' is the charge on an electron. 20 such balls are put in a cylindrical box and sealed. The total charge in the box will be ___ Coulombs.

Answer 1

When a particle carries a charge X, and n such particles are present in a system, the total charge on the system will be $n\times X$
Similarly, when n particles, each carrying a charge X, and m particles, each carrying a charge Y, are present in a system, the total charge of the system will be( $n\times X+m\times Y$).
Hence, total charge will be $20\times \left(e\right)Coulomb=20eCoulombs$